Field of the Invention
The present invention relates to a method for joining two components of a medical instrument, a use of an iron-based solder, and a medical instrument.
Description of the Background Art
Medical instruments, in particular invasive medical instruments, which are intended to be introduced into a human or animal body, are subject to special requirements. For reasons of mechanical and thermal loading, such instruments are often produced using metallic materials. In particular, the materials forming the outer surfaces of the instrument have to be biocompatible. If, for structural reasons, the medical instrument is made up of a plurality of individual components, a permanent connection of the components to one another is necessary. The connection has to meet the required strength and also provide sufficient resistance to chemical and thermal influences and satisfy the demands of biocompatibility. If the components connected to one another result in the formation of a cavity in which sensitive or non-biocompatible parts are accommodated, the connection of the components also has to be fluid-tight, for example in order to avoid entry of bodily fluid or of cleaning liquid into the cavity. These requirements apply even more in the case of reusable medical instruments, which have to be suitable for cleaning and sterilizing, in the process of which they are exposed to chemically aggressive substances and, during autoclaving, to an elevated temperature and elevated pressure.
DE 31 19 725 C2 discloses a laryngoscope spatula, which is constructed from two L-shaped elongate profiled members which are fitted together with a mutual overlap and soldered onto each other. Protruding studs are formed on the contact edges of the L-shaped elongate profiled members and engage in grooves formed in the other elongate profiled member, such that a mutual hold is achieved after the elongate profiled members have been fitted to each other. The profiled members are then fixed to each other by resistance-welding, and the remaining gaps are closed by hard soldering.
According to DE 33 17 831 C2, a laryngoscope spatula has a Z-shaped profile and an L-shaped profile, wherein the connection between a first limb of the Z-shaped profile and a central web wall with a shorter limb of the L-shaped profile is configured as a weld seam, which is then finely ground and finely polished. The connection point of a second limb of the Z-shaped profile to the longer limb of the L-shaped profile is produced in a soldering process using so much solder material that a pronounced radius of rounding and a surface substantially free of gaps are obtained.
EP 2 151 185 B1, which corresponds to U.S. Pat. No. 8,267,856, and which is herein incorporated by reference, discloses a laryngoscope spatula with a spatula blade, wherein the spatula blade is produced by provision of an upper shell and a lower shell which each have, in cross section, a first portion and two mutually oppositely extending second and third portions, the second and the third portions of the upper shell and the lower shell are placed flat on each other, and the upper shell and the lower shell are firmly connected to each other by joining of the second and third portions. The upper shell and the lower shell can be soldered peripherally to each other at contact edges forming mutually adjoining edges of the second and third portions.
To connect the individual parts of a conventional laryngoscope spatula by soldering, a copper-based solder is often used. Since copper is not biocompatible, spatulas produced in this way are usually additionally welded and chromium-plated, which entails additional production costs. Moreover, the use of a nickel-based solder is known. On account of the flow characteristics of the nickel-based solder, and in order to obtain a uniform surface, the soldering process is carried out using anti-flux which, however, can cause damage to a furnace in which the soldering takes place and in which the anti-flux evaporates. In addition, only a small gap can be bridged by a nickel-based solder, a rough and porous surface is often obtained, and, furthermore, it is not easy to weld over a soldering seam that has been produced with a nickel-based solder. Other methods for producing cohesive joins, for example laser welding, on the other hand have the disadvantage that the weld seams thereby produced, in particular quite long weld seams, are often not vapor-tight; a vapor-tight configuration of weld seams is necessary, however, for an autoclavable medical instrument that has a cavity containing sensitive electronic and/or optical parts.
DE 31 45 944 C2, which corresponds to U.S. Pat. No. 4,436,697, discloses a soldering alloy composed of 25 to 35% iron, 15 to 25% chromium, 3 to 6% silicon, 1 to 4% molybdenum, with the remainder cobalt, and used to solder parts of dental prostheses that were made from a cobalt/chromium alloy.